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Tokyo, Japan (CNN)Heavy rains were expected through Sunday after Japan's Kyushu region was struck by twin earthquakes, hampering the search for survivors and forcing nervous residents into crowded evacuation centers.

At least 32 people have died in the latest Kyushu earthquake, according to Kumamoto Prefecture's disaster management office. The magnitude-7.0 quake hit early Saturday.

Prime Minister Shinzo Abe described the search for survivors amid piles of rubble as a "race against the clock," noting that bad weather had conspired with the devastating quake, its aftershocks and the threat of landslides to make a dire situation worse.

In a Sunday morning press briefing, Abe said he received an offer of help from the U.S. military but it was not urgently needed yet. Japan has deployed 25,000 self-defense forces to the rescue effort, Suga said.

"We're racing against the clock," Abe said. "(We) will provide more personnel if necessary."

Japan quakes by the numbers

Deaths linked to Thursday's quake: 9

Deaths linked to Saturday's: 32

Total deaths: 41

Total injured: 968

Evacuated: More than 91,700

Homes destroyed: 90

Homes damaged: 775

Timeline:

Thursday at 9:26 p.m.: 6.2-quake about 4.3 miles from the city of Ueki

Friday at 12:03 a.m.: 6.0-quake hits about 3.7 miles east of Uto.

Saturday at 1:25 a.m.: 7.0-quake hits about 0.6 miles from Kumamoto-shi.

Sources: Kumamoto Prefecture's disaster management office; USGS.

Residents were already on edge after a 6.2. quake rattled the area two days earlier, killing nine people. The combined death toll has reached 41.The two earthquakes left 968 people injured, according to the disaster management office.

"This is the worst thing that could happen to us," said Shigeru Morita, an official in the town of Mashiki, Kumamoto Prefecture.

The latest and most powerful earthquake struck near the city of Kumamoto, toppling buildings and bridges, shredding sections of landmarks into piles of debris, and sending frightened residents fleeing from their homes and into the night.

"The first earthquake was very big," said Osamu Yoshizumi, the senior chief of international affairs in Kumamoto. "We thought it was the big one."

That initial earthquake was a "foreshock" to the latest one, according to USGS.

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A bigger tremor would come overnight Friday.

"When the second earthquake came everything shook and I thought I might die," said Taiki Hishida, 38, who evacuated with his wife and two young children to a crowded shelter in Mashiki.

Samuel Borer, a U.S. citizen living in Kumamoto, said the latest quake struck at about 1:30 in the morning.

"It was just pitch black in the middle of the night and everything just started to go wild," he said.

Noel Vincent went through both earthquakes.

"This extremely intense shaking began," he told CNN International. "And whereas the first earthquake was more of an up-and-down type of shaking, this was a side-to-side shaking. I can't comment on what that is seismologically but I can tell you it was very intense and I feared for my life."

Television images and photos showed empty shelves at supermarkets and stores, leaving many evacuees to line up for food and water at shelters.

"There wasn't actually enough food for everyone, which was the only problem," said Borer, speaking at an elementary school being used as a shelter. "Most of the food went to the elderly and children first."

Kumamoto Prefecture continues to experience aftershocks, with about 165 so far.

"I feel every aftershock," said Yoshizumi, who was working from the city hall building in Kumamoto. "It's swaying here every hour."

Rescue efforts

Photos:Earthquakes strike Japan

Rescuers prepare to remove the body of a woman found in a house destroyed by a mudslide in Minamiaso on Tuesday, April 19, in the aftermath of a 7.0-magnitude quake on Kyushu Island. The same region was hit by a 6.2-magnitude quake on Thursday, April 14.

Rescue workers take care of a woman suffering from shock at the evacuation center at the Mashiki Town Gymnasium on Saturday, April 16, in Kumamoto, Japan.

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A severely damaged building in Kumamoto leans to one side on April 16 after the earthquake.

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Medical staff prepare to evacuate patients from the hospital in Kumamoto City on April 16, over fears it could collapse as a wave of aftershocks hit the area.

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A road damaged by the 7.0 magnitude earthquake is seen on April 16 in Mashiki, Kumamoto, Japan.

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A police rescue team searches a damaged house for earthquake survivors Friday, April 15, in Mashiki, Japan.

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A woman cleans up in front of her collapsed house in Mashiki on April 15.

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A house in Mashiki teeters after the quake.

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A man takes a picture of a damaged stone wall at Kumamoto Castle, in the city of Kumamoto, on April 15.

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Smoke rises from burned houses in Mashiki on April 15.

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A woman rides a scooter in front of a collapsed house in Mashiki on April 15.

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An aerial view shows damage at Kumamoto Castle on April 15.

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Kumamoto Castle is a major tourism destination and one of Japan's important cultural properties.

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A resident passes by a toppled vending machine in Kumamoto on April 15.

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A man stands in front of his collapsed house in Mashiki on April 15.

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A rescue worker carries an 8-month-old girl after she was pulled from rubble in Mashiki on April 15.

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CNN International's Matt Rivers, reporting from an evacuation shelter, said the aftershocks are creating great anxiety among rescuers and residents.

"You're seeing people assigned here from one of two sorts of tracks," he said. "On the one hand, people who had their homes destroyed so they have nowhere to go. (But) the reality is that most people inside this evacuation shelter here are afraid to go home. They're not sure that maybe there might be another aftershock."

The aftershocks also could hamper rescue efforts as emergency workers attempt to pull out people trapped in the rubble. TV Asahi showed crews crawling over a collapsed roof in an attempt to find an elderly couple. An 80-year-old man was rescued from the rubble, according to CNN affiliate TV Asahi.

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The tremors appear to have caused extensive damage, overturning cars, splitting roads and triggering a landslide as shown by TV Asahi footage. Television images showed flattened houses, shards of broken glass and debris piled onto the streets and people huddled outside. Nearly 92,000 people have evacuated, according to the prefecture's disaster management office.

The Kumamoto government has opened more than 100 evacuation centers for residents and has started handing out food, water and blankets, Yoshizumi said.

Kumamoto Castle, a famous site in Japan built in the early 17th century, is badly damaged, he said.

Vincent told CNN he had an annual pass and would visit the castle each month. He described extensive damage to a retaining wall and a turret at the castle.

"I was just devastated to see the damage," he said. "It's just all surreal. I can't really quite process it. ... It's such a shame to see ... a treasure like that, a national treasure like that fall to pieces."

Hundreds treated

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The Red Cross treated more than 1,000 people in the Kumamoto area Friday, but the organization said it anticipates the number will increase following Saturday's earthquake.

The most serious injuries were to people cut by glass or in collapsed houses, said Nobuaki Sato, director of the International Relief Division at the Japanese Red Cross.

"We don't know what is happening in the whole disaster area because it is a remote mountain area and some big bridges were down and many landslides were found, so we were working around the clock and are making assessments," Sato said. "But so far the road access is not easy to the remote areas."

Japan's Fire and Disaster Management Agency said 7,262 people have sought shelter since Friday in the Kumamoto Prefecture.

Abe called off a planned visit to Kumamoto on Saturday. His office told CNN the prime minister would instead spearhead efforts from Tokyo. The country's air force planned to send six planes and nine ships to Kumamoto to deliver food, blankets and all emergency necessities.

Japan received offers of support from other nations.

PM: Deeply saddened by news of a second earthquake in #Japan. UK ready to do what it can to support Japan's response in #Kumamoto.

Japan's 'Ring of Fire'

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The shallow depth of the latest quake and the dense population of where it struck could prove to be devastating, according to experts.

"No question, this is a large and very important earthquake," said Doug Given, a geophysicist with the U.S. Geological Survey, "and it will do a lot of damage."

The four islands of Japan are on the edge of what's traditionally been known as the 'Ring of Fire'" -- a stretch along parts of the Pacific Ocean prone to volcano activity and earthquakes.

Victor Sardina, a geophysicist in Honolulu, Hawaii, told CNN the latest quake was about 30 times more powerful than the first one near Ueki. He predicted "severe, serious implications in terms of damage and human losses."

Japanese media reported a small-scale eruption of Mt. Aso on Saturday morning. It was unclear whether it was related to the earthquake, according to the Japan's meteorological agency.